In wireless communication systems, many users communicate over a wireless channel. For example, code division multiple access (CDMA) modulation technique is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA) and frequency division multiple access (FDMA) may be used as well. A user receives wireless service from the wireless communication system using a mobile station, which may refer to a cellular phone, user equipment (UE), a wireless communication device, or a wireless terminal.
In a wireless communication system, data may be modulated into symbols using Quadrature Amplitude Modulation (QAM). Each QAM symbol is obtained by mapping multiple data bits onto a single constellation point in a QAM constellation. Because each QAM symbol carries multiple data bits, QAM can be used to increase data throughput.
At a receiver, a QAM symbol is detected based on the magnitudes of in-phase and quadrature components of the received signal using a detection technique. An example of a non-linear detection technique is minimum square error estimation (MMSE), which requires an accurate estimation of the signal magnitude and noise power, and is thus susceptible to error in the presence of multi-user interference and noise. Therefore, systems and methods that provide accurate symbol detection in the presence of multi-user interference and/or noise are desirable.